Xacro unless property check -> error

Running this file with roslaunch command, and passing the cam_serial and cam_index. But I'm getting error:
Invalid roslaunch XML syntax: unbound prefix: line 3, column 0
The traceback for the exception was written to the log file

Why is that extra pair of <> there? The <... some xml code here ...> on the wiki/xacro - Conditional Blocks is meant as an example. You are expected to replace all of it, including the <>.

Same goes for the contents of your value attribute on the xacro:unless element.

Also: the expression inside a unless or if should evaluate to a boolean (so true or false). Now 21665943 will probably evaluate to true, but I'm not sure that is what you are after. I would expect to find something like value="something == something".